1. Field of the Invention
The present invention relates to an device which uses a quantum effect.
2. Description of the Prior Art
Owing to the progress of semiconductor techniques, the miniaturization of devices and the high integration of devices have been progressing. Due to the miniaturization of the devices, the normal operation of the devices is being prevented by various physical limits including the quantum effect. Accordingly, it is necessary to develop a new device which different from the conventional transistor.
Among the devices to carry out signal processing by propagating electron signals, conventional charge transfer devices having functions carried out by spatially transferring electric charges including, for example, Charged Coupled Devices (hereinafter abbreviated as CCDs) were proposed by Boyl and Smith, Bell Research Institute, U.S.A. in 1970. FIG. 21 is a structural view of a CCD device which is a conventional charge transfer device. In FIG. 21, element 140 is a p-type silicon substrate; element 142 is a silicon oxide film, and element 144 is an electrode; the device has an MOS capacitor integrated structure. FIG. 22 shows a schematic view of a section of a 2 bit n-channel CCD device, wherein element 140 is a p-type silicon substrate; elements 141 and 143 are n-type doping layers; element 142 is a silicon oxide film, and element 144 is an electrode. Alphabetical symbols in FIG. 22 show the control signals on each electrode 144. ID denotes an input signal to an input diode; IG denotes an input control electrode signal; .phi.1, .phi.2, and .phi.3 denote control signals; OG denotes an output control electrode signal, and OD denotes an output diode signal. FIGS. 23(a) and 23(b) respectively show a schematic view of the section of the CCD device shown in FIG. 22 and a time chart of the control signals such as ID, IG, etc. FIGS. 24(a) and 24(b) respectively show a schematic view of the section of the CCD device shown in FIG. 22 and an explanatory view showing a time transition of the internal potential and the state of charge transfer. Each time t1-t7 of FIG. 24(b) corresponds respectively to t1-t7 as shown in the time chart of FIG. 23(b).
Next, the principle of the charge transfer of the CCD device of FIG. 22 is briefly explained. In FIGS. 23(a)-23(b) and FIGS. 24(a)-24(b), when t=t1, because the input diode signal ID is applied in the inverse bias direction, no signal charge (electron which is decimal carrier) is injected even when the input control electrode signal IG and the control signal .phi.1 are ON. At t=t2, the input diode is biased in the normal direction, and an electron starts to be injected to the potential well under the initial electrode to which .phi.1 is applied, the electron being injected until the level becomes the same as the potential of the input diode. At t=t3, the input diode is again inverse biased. Subsequently, using the control signals .phi.1, .phi.2, .phi.3 of the control electrode, the potentials under the control electrode are varied from left to right in order, by which it is known that the signal charges are also transferred from left to right.
On the other hand, in 1984, a three-terminal quantum device for arranging the quantum dots in parallel was proposed by Reed, et. al of Texas Instruments, Inc., U.S.A. (U.S. Pat. No. 4,912,531: Three-terminal Quantum Device). FIG. 25 is a constitution view of conventional quantum device. In FIG. 25, elements 202 and 204 are quantum dots. Elements 206 and 210 are source and drain electrodes. Also, the quantum dot 202 is connected to the control electrode 208. FIGS. 26(a) and 26(b) show energy structural views when the bias is not applied to the source/drain terminals and when it is applied, respectively. By appropriate bias, the dissipated energy levels between the quantum dots 202 and 204 agree, and the signal electron is propagated from the source to the drain. By further combining a plurality of these quantum dots in an organic state, a device using the quantum dots and having a logic operating function is proposed.
On the other hand, the present applicant has already proposed the methods for producing quantum devices in Japanese Patent Application Nos. HEI3-180830-180834 and the like. When these production methods are applied, as the method for producing the device having the quantum dot or quantum wire, the following method is considered. FIGS. 27(a)-27(e) show a process for forming a conventional device. In FIGS. 27(a)-27(e), element 321 is a ridge line formed by anisotropic etching a silicon substrate; element 322 is a one-dimensional quantum wire; element 323 is a separated oxide; element 324 is a resist; element 325 is a silicon oxide; element 326 is a one-dimensional quantum wire; element 327 is a quantum dot, and element 328 is a tunnel oxide film. With respect to the forming process of the quantum device constituted as above, the flow for making it is explained below.
In FIG. 27(a), a ridge line 321 is formed by anisotropic etching the silicon substrate. In FIG. 27(b), a separation oxide film 323 is formed on the lower part of the ridge line 321. In FIG. 27(c), a resist 324 is formed as an oxygen ion injection mask. In FIG. 27(d), oxygen ion injection is carried out to form a silicon oxide 325. In FIG. 27(e), the resist 324 is removed to give a one-dimensional quantum wire 326, a quantum dot 327, and a tunnel oxide film 328. Propagation takes place by the resonant tunnel effect.
However, according to the conventional semiconductor device, as the size of the device enters into the region smaller than 0.1 .mu.m, an improvement in the device performance according to the simple scaling rule to start to be inhibited due to various problems. This is due to the fact that: (1) the driving ability and controlling ability of the device no longer increase due to miniaturization but rather decrease; (2) nevertheless, parasitic loads such as wiring, device separation, etc. become large, and losses are caused to the propagation of electronic signals to make the normal device operation impossible.
Further, in the charge transfer device as above, the transfer of charge takes place by the spreading of the decimal carriers, and there has been a problem in that the improvement of the transfer rate is limited.
Moreover, the device formed by the combination of the quantum dots only shows a large loss of signal in the case where an electronic signal is propagated at a low loss for a certain distance and is connected to the device of the next step. Further, it cannot store information as in the conventional device.
In view of the above problems, the present invention provides a transfer device of a signal electron which has a high speed and small losses by positively utilizing the quantum effect which appears in the region not exceeding 0.1 .mu.m and carrying out electron propagation by utilizing the resonant tunneling effect between the quantum levels separated in the one-dimensional quantum wire and zero-dimensional quantum dots.